Domestic fowl such as chicken and turkeys usually are subjected to scalding before their feathers are removed. In the scalding process the carcasses of recently-killed fowl, hereinafter referred to as "birds", are subjected to hot water which wets and loosens the feathers relative to the carcass. Subjecting the birds to hot water also helps remove grease and contamination from the exterior of the bird, which makes easier the subsequent defeathering or plucking of the bird.
The conventional approach to scalding birds in commercial poultry-processing operations is to immerse the recently-killed bird in a tank of hot water. This immersion takes place while the birds are suspended from shackles moving along a conventional overhead conveyor line. The line passes above a dip tank filled with water heated to the desired temperature, and the conveyor line moves downwardly to lower the birds into the water. The birds traverse the tank while immersed in the water, and then emerge from the tank as the conveyor line moves upward and carries the birds on to the picking machinery.
Because each bird can release fecal matter or other body fluids to the water while the bird is immersed in the dip tank, the water in the dip tank soon becomes highly contaminated with feathers, dirt, blood, and fecal matter from the birds. This unsanitary condition becomes increasingly bad as successive birds are dipped in the scalder. In practice, most poultry processing plants frequently drain the scalder tank, thereafter cleaning the scalder tank, refilling it with fresh water, and heating the fresh water to the desired scalding temperature, which can range from about 115.degree. F. to about 140.degree. F. depending on whether soft scalding or hard scalding is desired. The task of cleaning a dip-tank scalder is recognized as one of the most unpleasant tasks in a poultry processing plant. Moreover, the entire processing line must be shut down for the time taken to drain and clean the scalder, and then to heat the refilled water to the desired scalding temperature. This cleaning operation also is wasteful of energy through the need of periodically discarding the hot water in the tank.
The problems associated with the conventional dip-tank scalder have not gone unnoticed, and efforts to overcome the problem are known to the prior art. These attempted solutions, however, have not proven successful and thus have not found general acceptance in the industry. One such proposal is known as the steam scalder wherein the birds are subjected to an environment of steam or a steam-water mixture instead of dipping the birds in a tank. It has proven difficult to control the temperature to which each bird is subjected in a steam scalder, especially where only soft-scalding is desired. Applying excessive heat to the bird during the scalding operation can cause spotting or otherwise damage the skin, impairing the appearance and reducing the commercial value of the bird. Other proposed replacements for dip scalders employ nozzles positioned to spray hot water on the birds. The hot water used in any scalder must be recycled as a practical matter, due to the unacceptable cost otherwise associated with constantly heating fresh cold water instead of adding incremental heat to recirculating hot water. Because the recirculating water soon contains feathers and other particulate matter which tends to lodge in and clog the spray nozzles, the spray scalders of the prior art have experienced substantial downtime and have not found practical acceptance.